+ mm-page_isolation-do-not-take-slab-pages-for-free.patch added to mm-unstable branch

+ mm-page_isolation-do-not-take-slab-pages-for-free.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm: page_isolation: do not take slab pages for free
has been added to the -mm mm-unstable branch.  Its filename is
     mm-page_isolation-do-not-take-slab-pages-for-free.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-page_isolation-do-not-take-slab-pages-for-free.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Josef Bacik <josef@toxicpanda.com>
Subject: mm: page_isolation: do not take slab pages for free
Date: Tue, 27 Oct 2026 16:46:33 +0100

page_is_unmovable() regards a page with a reference count of zero as free
or about to be freed. Since slab allocates frozen pages, they will
be wrongly considered to be freed if order 0 (higher-order compound
pages are caught earlier).

If such slabs are the only unmovable pages of a memory block, memory
offlining now isolates the block, this can lead to offline_pages()
looping without progress.

Thus detect the slab pages as removable to return -EBUSY, as would
happen before commit 9aec2fb0fd5e ("slab: allocate frozen pages").

Link: https://lore.kernel.org/20261027-pgalloc-ai-hotfixes-v1-7-9c7d1aca801e@kernel.org
Fixes: 9aec2fb0fd5e ("slab: allocate frozen pages")
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Assisted-by: LLM
Cc: Zi Yan <ziy@nvidia.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Brendan Jackman <brendan.jackman@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Gregory Price (Meta)" <gourry@gourry.net>
---

 mm/memory_hotplug.c |    7 +++++++
 mm/page_isolation.c |    7 +++++++
 2 files changed, 14 insertions(+)

--- a/mm/memory_hotplug.c~mm-page_isolation-do-not-take-slab-pages-for-free
+++ a/mm/memory_hotplug.c
@@ -1847,6 +1847,13 @@ static int scan_movable_pages(unsigned l
 		if (PageOffline(page) && page_count(page))
 			return -EBUSY;
 
+		/*
+		 * A page that was allocated, but was not a slab page yet, when
+		 * its pageblock was isolated.
+		 */
+		if (PageSlab(page))
+			return -EBUSY;
+
 		folio = page_folio(page);
 		if (!folio_test_hugetlb(folio))
 			continue;
--- a/mm/page_isolation.c~mm-page_isolation-do-not-take-slab-pages-for-free
+++ a/mm/page_isolation.c
@@ -75,6 +75,13 @@ bool page_is_unmovable(struct zone *zone
 	}
 
 	/*
+	 * Slab pages are frozen: do not take their reference count of zero
+	 * for that of a free page.
+	 */
+	if (PageSlab(page))
+		return true;
+
+	/*
 	 * We can't use page_count without pin a page
 	 * because another CPU can free compound page.
 	 * This check already skips compound tails of THP
_

Patches currently in -mm which might be from josef@toxicpanda.com are

mm-page_alloc-dont-undo-a-racing-start_isolate_page_range.patch
mm-page_alloc-clear-private-of-deferred-free-pages.patch
mm-page_frag-refill-the-cache-for-large-fragments.patch
mm-page_alloc-keep-the-pagesets-of-an-empty-zone.patch
mm-page_alloc-pass-zone-pointer-to-trace_reclaim_retry_zone.patch
mm-compaction-trust-zone-contiguous-only-in-the-span.patch
mm-page_isolation-do-not-take-slab-pages-for-free.patch
mm-memory_hotplug-resize-zones-under-their-seqlock.patch
mm-page_alloc-check-pageblock-pfns-under-span-seqlock.patch